The general goals of this project are 1) to define taxoNomically, the microbial composition of cariogenic and non-cariogenic dental plaques; 2) to determine the metabolic characteristics of cariogenic and non-cariogenic plaques and 3) to evaluate the effect of sodium fluoride on the microbial composition, metabolism and cariogenicity of cariogenic dental plaques. The investigation will be divided into 3 phases. First, a longitudinal analysis of the oral microflora and the sucrose metabolism of saliva will be conducted with human volunteers during periods of high and low sucrose consumption. Half of the volunteers will be caries-free individuals and half caries susceptible individuals. This analysis should indicate which subjects harbor a potentially cariogenic oral microflora as well as allow a correlation between sugar intake and oral microbial profile to be made. In the second phase of the project the same subjects will wear a removable appliance containing enamel surfaces on which plaque can develop. Half of the experimental plaques on each appliance will be exposed to cariogenic substrates several times a day for 3 weeks and half simultaneously exposed to a control solution. The microflora and sucrose metabolism of the plaques will be evaluated periodically and the cariogenicity of the plaques determined by enamel microhardness measurements. These date will allow a correlation between the oral microbial profile of the subjects in the first phase of the project and the ability of the particular types of microbiota to induce experimental dental caries. This information along with the data from the first phase should establish what microbial combination will most likely produce dental caries, and it should facilitate a prediction of the cariogenic, or lack of cariogenic potential of the microflora. The third phase of the project will be an investigation of the effect of a potentially cariostatic agent, sodium fluoride, on the microflora, sucrose metabolism and cariogenicity of experimental plaques. The removable model and the same human volunteers will be used in these experiments. The results of the third study should reveal how this cariostatic agent can be used most effectively to alter cariogenic activity and the mechanisms of cariostasis in the experimental model.